We recently identified and isolated an extracellular toxin produced by Legionella pneumophila. The goal of this research is to continue to study this toxin in order to obtain the reagents and background information which are a necessary prerequisite for future studies on the possible role of this toxin in Legionnaires' disease. Specifically we intend to (1) study conditions for the production of L. pneumophila toxin in vitro in order to maximize its yield and facilitate its purification, (2) adapt procedures we have utilized in purifying small amounts of the toxin to large scale purification in order to obtain sufficient toxin to be characterized, (3) characterize the purified toxin chemically and biologically, (4) continue to study the effect of this toxin on human PMN's and initiate studies or the effect of the toxin on human monocytes, and alveolar macrophages (viability and function) and (5) continue to investigate the mechanism of action of the cytotoxin by examining its effects on the physiology and metabolism of sensitive tissue culture cells.